This invention relates, in general, to surface micromachined structures, and more particularly, to a method of fabricating surface micromachined structures.
Surface micromachined structures are used for a wide variety of applications, including accelerometers and other actuators and sensors. These micromachined structures are fabricated by depositing and patterning a sacrificial or release layer on a substrate, depositing and pattering a polysilicon film to form a dynamic element, forming a metal contact to the dynamic element, and removing the release layer to leave the dynamic element partially supported or free standing above the substrate surface.
After the release layer has been removed, the dynamic element is fragile and can be damaged by further processing. Therefore, it is desirable to remove the release layer at the end of the processing. However, if the metal contact layer is comprised of aluminum, a photoresist layer has been used to protect the metal contact during removal of the release layer. Using a photoresist layer is disadvantageous because the photoresist layer must be removed by a solvent after the dynamic element is released and fragile. Photoresist removal also involves a cleaning step in which the substrate must be spin dried. Damage to the dynamic element will more than likely result at this time.
To solve the above problem, a metal contact layer comprised of gold rather than aluminum has been used, because gold is compatible with the etchant used to remove the release layer, and does not require protection. The use of gold, however, is undesirable because it is not the standard metal used in semiconductor fabrication, and it is more expensive than aluminum.
In the past, separation of individual die has been done after processing of the device is complete. Separation of individual die is accomplished by a sawing operation. Saw vibration can cause damage to the fragile micromachined structures after the release layer has been removed. There are also contamination problems that result from debris produced during the saw operation. It would be desirable to prevent these contamination and damage problems.